Connectivity in the life histories of fishes that use estuaries

Historically, coastal fisheries biology has focused on the theme of estuarine dependency with emphasis on microhabitat use. Ironically, however, few fishes that we associate with estuaries are in fact obligatory users. What then are the causes and consequences of estuarine habitat use? At the Estuarine Research Federation 2003 Seattle Meeting, we explored ‘‘connectivity’’ in the life cycles of fishes and invertebrates that use estuaries. Connectivity here refers to the dependence of fish production and population dynamics on dispersal and migration among multiple habitats. Further, we propose that spatial dynamics of estuarine and coastal fishes, by dint of their diversity, represent key resiliency mechanisms in fisheries and habitat management. At first blush, connectivity seems an unfortunate term in describing the spatial dynamics of estuarine-associated fishes. In many disciplines it has become jargon and trite. The term emerged with telecommunications and simply means the ability to connect or interconnect: a fairly trivial attribute of fish life cycles. On the other hand, the second more technical definition in the Oxford Dictionary describes a more interesting element to connectivity: ‘‘. capacity for the interconnection of platforms, systems, and applications.’’ Capacity implies the potential storage and use of information that is differentially transmitted across platforms, systems, and applications. Important synergism occurs in the diversity of sources, routes, and destinations of information in systems of connectivity; so too in the complex life cycles of fishes. Here, we suggest that connectivity implies the enhanced storage of genetic and energetic pools due to variable migration and dispersal patterns across habitats and ecosystems. The so-called storage effect, i.e., increased population resiliency due to life history variations, has emphasized variations in demographic schedules (Chesson, 1994; Secor, 2000; Fromentin and Fonteneau, 2001; Francis, 2003). We propose that variance associated with spatial dynamics (i.e., connectivity) as a key component of the storage effect. Before we move on to complex life cycles, there are other definitions of connectivity in aquatic ecosystems,